Chinese authorities have vowed to crack down on protesters in a central Sichuan province city after riot police clashed with hundreds of people rallying against a planned new metals plant.
In unusually strong language, Shifang city police warned citizens on Tuesday that they would be "severely punished" if they sought to continue the "illegal" protests over environmental concerns.
The violence erupted on Monday when, according to the official account, protesters in the city of around 430,000 attacked government offices with bricks and stones, smashed cars, and clashed directly with police and government employees.
The city government has said only 13 people were injured.
"Anyone who has incited, planned or organised illegal gatherings, protest marches or demonstrations or those who have engaged in smashing and looting ... will be punished severely," the police said. "Anyone using the Internet, mobile text messages and other methods to incite, plan or organise illegal gatherings, protest marches or demonstrations must immediately stop their illegal activities."
Photos of the unrest that were posted online but which could not be verified appeared to show hundreds of police in riot gear clashing with protesters.
Others showed hundreds of protesters marching through the streets carrying banners calling for the planned factory to be scrapped.
Hong Kong's Ming Pao newspaper reported that one high school student had died.
The factory, owned by the Shanghai-listed Sichuan Honda company, would process molybdenum-copper alloy, and residents said on web postings they were scared of the damage it would do to the local environment.
While warning against further protests, the local government also issued a statement on Monday saying construction of the factory had been stopped.
Calls to the Shifang police and government went unanswered Tuesday.
A Shifang resident, when contacted by the AFP news agency, said roads in the city remained blocked by police on Tuesday but it was unclear whether there were further protests.
Social unrest is a major problem for China's communist rulers, who are struggling to deal with anger across the vast nation of 1.3 billion people over issues such as environmental degradation, rising inequality and corruption.
Protests similar to the one in Shifang are reported regularly.